Hydrogen Safety System Summary
Elwyn Baynham, Tom Bradshaw , Yury Ivanyushenkov
Applied Science Division,
Engineering and Instrumentation Department
RAL
MICE Collaboration Meeting, Osaka, August 1-3, 2004
1
Scope
• Status of hydrogen absorber and system safety
• Hydrogen system:
- changes in the system according to the Safety Review Panel
recommendations;
- ongoing work on safety issues;
• Hydrogen absorber/system operation:
- instrumentation and control.
• Hydrogen R&D
2
Status of hydrogen absorber and system safety
Safety = Safe Design + Safe Operation
Design:
• Internal safety review
- passed
( many useful comments, response is ready)
• Preliminary HAZOP
• Instrumentation
- done
- to be
implemented
Operation:
• Operation analysis
• Safety system analysis
• R&D stage
• Operation manual
- started
- started
- to be done
- to be written
Final safety review – to be passed
3
Changes in MICE hydrogen system
AFC Safety Review Panel recommendations are implemented:
• Buffer vessel is removed from venting path.
• Vent manifold is added. The manifold is filled with nitrogen.
• Venting lines are separated.
Other changes:
• Buffer vessel is added in between absorber vessel and hydride bed:
- together with liquid hydrogen vessel and hydrogen condensation pot forms
a quasi-closed system;
- improves time response of safety devices in case of catastrophic failure.
• Ventilation system is removed. Most of the equipment is now sits
under hydrogen extraction hood.
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MICE hydrogen system
High level vent
High level vent
Non return
valve
Vent manifold
0.1 bar
Hydrogen zone 2
Vent
outside
flame
arrester
Vent manifold
H2Detector
Extract hood
VP2
PV8
P
PV7
P
PV2
Buffer
3
vessel 1 m
Hydrogen
supply
P
P1
P
PV1
Metal Hydride
storage unit
(20m3 capacity)
1 bar
Tbed
PV3
Chiller/He
ater Unit
PV4
Fill valve
P
Pre-cooling
Out In
HV1
P2
P
0.5 bar
Liquid level gauge
P
P
P
0.9 bar
P3
Internal Window
P
HV2
Purge valve
P
LH2 absorber
H2 Detector
Safety windows
Vacuum
Purge valve
HV3
Vacuum vessel
Nitrogen
supply
0.9 bar
PV6
Helium
supply
0.5 bar
VP1
P
Pressure
gauge
P
Pressure
regulator
Valve
Pressure
relief valve
Non-return
valve
Bursting disk
VP
Vacuum pump
5
Safety issues: Ongoing work
• Pressure rise rate calculations
• Valves
• Hydrogen sensors
• Control
6
Operation issues: Ongoing work
• Operation from cryocoolers
• Instrumentation and control
7
Hydrogen absorber instrumentation
Instrumentation to be implemented into absorber design:
• Hydrogen level sensor/s:
- their functions (what do we need them for)?
- continuous/ discrete?
- how many and where?
• Temperature sensors:
- their functions ?
- how many and where?
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Hydrogen level sensors
Continuous level sensor
Point level sensors
24-M4
4-M6
24-M8
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Cryogenic liquid level sensors from AMI
The capacitance-based liquid level sensor, used in conjunction with
the Model 185 and 186, is manufactured of stainless steel tubing.
Upon request, special assembly techniques can be applied for
sensors required for liquid oxygen or hydrogen measurement _
including minimization of oils during construction and no use of
epoxies. Sensors can be supplied in single-section overall lengths
of up to 30 feet. Multi-section lengths in excess of 50 feet are
available upon request.
Three standard sensor mounting configurations are available. The
typical configuration includes a hermetically sealed BNC connector
with an adjustable 3/8" male NPT nylon feed-through. For higher
pressure or vacuum applications, a welded stainless steel 3/8"
male NPT fitting or conflat flange fitting is available. Twelve feet
of connecting coaxial cable and in-line oscillator/transmitter are
included with the sensor. With additional cable the sensor can
be remotely mounted over 500 feet from the instrument without
effecting performance.
Sensor options include:
1. Rugged service construction 1/2" or 3/4" OD
2. Miniature sensors of 3/16" and 1/4" OD
3. Radius bends up to 90°
4. Capacitance or RTD point sensing elements
Custom sensors are available from AMI to meet your individual
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Level sensor implementation
Continuous level sensor
Connector required
(Swagelok VCR Metal gasket
face seal fittings ?)
Can a sensor be manufactured to this shape ?
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What is known about metal hydride tank
Table 1
Hydrogen Storage Capacity
Tank number/system
The specification of the MH tank for RAL
20 Nm3
1
Tank Description:
Heat Transfer Medium
Water
MH Weight
155kg
Tank Structure
Dimensions
Tank Total Weight
Shell & Tube type
φ216.3×L1600（mm） ( not include attachments )
220 Kg
Operating Condition:
Charging Gas Component
Hydrogen of 99.99% purity
Charging Gas Pressure
1.2 barA
Hydrogen Charging Rate
70NL/min
(up to 90% of Storage Capacity)
Discharging Gas Pressure
1.2 barA
Hydrogen Discharging Rate
70NL/min
(up to 90% of Storage Capacity)
Utility Requirements:
Cooling Medium
Water
Below -10℃ （At 20L/min）
Heating Medium
Design Code
Certification
Above 20℃ （At 20L/min）
（AD Merkblaetter )
（Declaration of Conformity to Pressure Equipment Directive 97/23/EC
Certified by a Notified Body）
REFERENCE
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What is known about metal hydride tank (2)
φ
21
6.
3
Fig.1 Schematics and dimensions of the MH tank
(1810)
(1600)
140
Valve
Filter
Relief valve
2-Rc3/4
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What is known about metal hydride tank (3)
Fig.2 P-C-T curves of metal hydride for RAL
Hydrogen Pressure
(MPa)
17℃
100
30℃
0.12MPa
-1
10
10℃
-10℃
10-2
0
50
100
150
200
Hydrogen Content (cc/g)
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What is known about metal hydride tank (4)
Annotation by JSW:
Attached please find the temporary specification of a 20Nm3 metal hydride
(MH) tank, its sketch and the pressure-composition-temperature diagram of
the candidate MH alloy.
It would be better to explain the temperatures and pressures on charging and
discharging hydrogen, referring to the PCT diagram.
As you can see in the diagram (Fig. 2), it is possible for the alloy to
absorb hydrogen gas almost to its maximum capacity at 0 degC if the pressure
of hydrogen gas is maintained at 0.12 MPa. However, we are not yet sure of
the influence of pressure loss inside the tank under such a negative
pressure region. So, at the moment the charging temperature is specified to
be below -10 degC with 0.12 MPa of charging pressure (See Table 1.).
Then, you can see in the diagram (Fig. 2) that the MH alloy can discharge
almost all the hydrogen at +20 degC if the pressure is maintained at 0.17
MPa. To be on the safer side, the discharging temperature is specified to be
"above" +20 degC (See Table 1.). This means that the maximum internal
pressure of the MH tank is likely to be reached during the hydrogen gas
holding period if the water is stopped and the surrounding temperature
increases. However, even at +30 degC, the expected internal pressure is not
so high, approximately 1 MPa.
As a matter of fact, there will be an unknown factor, i.e., how accurately
we could control the materials properties when we newly manufacture an MH
alloy. Due to slight variations in the chemical composition and other
manufacturing parameters, the equilibrium temperature could vary by up to 5
degC for the same pressure. This could cause further changes in the
charging/discharging temperatures and consequently the internal pressure.
Since the relative plateau positions do not change, please assume that a
difference of more than 30 degC is needed between the charging and
discharging temperatures for the given charging and discharging pressures.
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Hydrogen R&D
Conceptual question: a small-scale rig vs. a full-scale prototype ?
Decision: go for a full-scale system which later will be used in MICE.
R&D goals:
• Establish the working parameters of a hydride bed in the regimes of
storage, absorption and desorption of hydrogen.
• Absorption and desorption rates and their dependence on various
parameters such as pressure, temperature etc.
• Purity of hydrogen and effects of impurities.
• Hydride bed heating/cooling power requirements.
• What set of instrumentation is required for the operation of the system?
• Safety aspects including what is the necessary set of safety relief valves,
sensors and interlocks.
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Hydride system test rig
High level vent
High level vent
Non return
valve
Vent manifold
0.1 bar
Hydrogen zone 2
Vent
outside
flame
arrester
Vent manifold
H2Detector
Extract hood
VP2
PV8
P
Mass
spectrometer
P
PV2
Buffer
3
vessel 1 m
Hydrogen
supply
PV7
P
M. F.M.
P1
P
PV1
Metal Hydride
storage unit
(20m3 capacity)
1 bar
Mass flow meter
Tbed
PV3
Chiller/He
ater Unit
PV4
Fill valve
P
HV1
Coolant
Out In
P2
P
0.5 bar
0.9 bar
P
P
P
P3
P
HV2
Purge valve
P
Test absorber
assembly
H2 Detector
Purge valve
HV3
0.9 bar
Nitrogen
supply
PV6
Helium
supply
0.5 bar
VP1
P
Pressure
gauge
P
Pressure
regulator
Valve
Pressure
relief valve
Non-return
valve
Bursting disk
VP
Vacuum pump
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Tchill
Next steps
• Finish pressure rise rates calculations
• Select safety devices
• Control system diagram
• Instrumentation defined and implemented into design
• Hydrogen R&D:
- find suitable place for hydrogen test area (MICE hall ?);
- timetable depends on funding
but would like to setup test rig in 2005.
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